This invention relates generally to parking brake vehicle actuators and, more particularly, to parking brake actuators having a variable ratio capability.
Many different types of actuators have been developed to operate vehicle parking brakes. Manual actuators utilizing both hand-operated and foot-operated input levers which actuate the parking brake through movement of a flexible cable are the most popular type in current use. In these actuators, the force exerted by the vehicle operator's hand or foot on the input lever is translated into an output force on the cable to apply the parking brake. A releasable latch, usually in the form of a pawl and sector, automatically latches the lever in the selected brake applied position.
In these manual parking brake actuators, the relationship of operator input movement to parking brake cable output movement (i.e. mechanical advantage) is dependent on several factors comprising the environment of the actuator lever relative to the operator. Some of these factors are lever arm size, hand or foot operation, lever travel space available, amount of input effort required to apply the parking brake, and operator positioning relative to the lever.
As a result of differing environments, some of these actuators utilize constant ratios of input lever movement to output cable movement. In others, a variable ratio of input lever movement to output lever movement is utilized to provide for relatively constant input effort as the output force requirements to further apply the parking brake increase. The input/output ratio will therefore vary depending on the requirements of a particular vehicle environment. Different vehicle environments dictate that different constant or variable ratios be utilized.
Heretofore, each different vehicle environment dictated use of a different actuator, which was usually developed specifically for a particular environment. As a result, scores of different parking brake actuators have been designed and are manufactured and in use.
It would be desirable to reduce the number of different parking brake actuators needed for the variety of different vehicle environments by developing a parking brake actuator which utilizes predominately standard parts common to all actuators.
It would also be desirable to develop a parking brake actuator that utilizes a standard basic actuator and a plurality of interchangeable inserts which adapt the actuator to the variety of constant and variable input/output ratio environments.